Learn how light can be converted into electricity through play
What you'll learn:
What the photoelectric effect is, and how the threshold frequency (or color) of the incident light impacts the current generated.
The photoelectric effect uses the energy from light to release electrons in a metal and create a current.
Learning the Photoelectric Effect with Kids.
What is the Photoelectric effect?
In physics, light isn’t just a wave. It is also a particle. This is called the wave-particle duality and leads to all sorts of interesting phenomena since light behaves as both at the same time. Why is that odd? Well, a wave extends over a large amount of space. There isn’t really a “position” it specifically has. While a particle has a very specific position.
The photoelectric effect happens when particles of light, called photons, hit a metal. Electrons hanging on to the outside of the metal can get knocked off if the photons hit them hard enough (that is, with enough energy). In this way, the photoelectric effect turns the energy of light shining on a material into an electrical current that can light a light bulb or drive a car.
How can I demonstrate the photoelectric effect to kids?
Demonstrating the photoelectric effect is difficult because the little packets of light, the photons, are very, very small. We can show what the photoelectric effect can do by using sunlight to drive a solar paneled car, but kids can’t actually see the photoelectric effect happening during that.
In this hands-on photoelectric effect demonstration kids will get to learn about the photoelectric effect and an important part of the photoelectric effect, the threshold frequency, through a hands-on experiment outlined below.
How to make a hands-on photoelectric effect demonstration for kids
- One the flat side of your box drill holes that are slightly larger than the ping pong balls.
- Wrap weather stripping on the inside of each hole.
- Fill ornaments with various amounts of sand and color accordingly (blue has the most sand, red has the least)
- Place ping pong balls on top of holes.
- Bop (or hammer?) the ping pong balls into the box using the ornaments.
Making a photoelectric effect demonstration.
1. Drill holes larger than the ping pong balls on a flat side of your box.
In our photoelectric effect demonstration, the electrons (ping pong balls) will be hit through the cardboard box (metal surface) leaving holes in their place. You want your holes to be larger than the ping pong balls (which act as our electrons) so we can install weather stripping to allow a little flexibility in the material. If we drilled holes just the right side the ping pong balls might stay for the first child playing with this experiment but would then be too large for the next child.
2. Wrap weather stripping on the inside of each hole.
Since our holes are too large to support the ping pong balls (our electrons in this project), we will glue weather stripping inside each hole. The weather stripping is a line of foam that can squish out of the way of the ping pong ball and regain its shape after. This allows the ping pong balls to be hit through the cardboard again and again.
3. Fill ornaments with various amounts of sand and color accordingly.
An important aspect of the photoelectric effect is the threshold frequency. Photons must have enough energy to knock out the electrons from the metal surface (which is played by our flat cardboard surface). To model that in this demonstration we are using plastic ornaments filled with different amounts of sand. We will be dropping the ornaments onto the ping pong balls. In this demonstration, heavier ornament (which represents a photon) would correspond to a more energetic photon (here it has more potential energy, while in the photoelectric effect it has more kinetic energy). The rainbow goes from low energy to high energy, that is red has a lower energy than purple. As you fill and color your ornaments the heavier ornaments should be colored blue/purple while the lighter ornaments are colored red.
4. Place ping pong balls on top of the holes.
We’re ready to set up our photoelectric effect demonstration for kids. Using a sharpie write an “e-” on all of the ping pong balls. This is a scientists symbol for electrons. Place each electron so it rests on a hole.
5. Play with your photoelectric effect demonstration
Using only the sand filled ornaments (or our photons), hit the electrons through the holes and into the cardboard box. A student will notice that some ornaments will not be able to knock the ping pong balls though. That is, some of the ornaments are too light to be able to hit the ball through the hole. This demonstrates the threshold frequency. In the next section, we will look at how this project demonstrates the photoelectric effect.
How this photoelectric effect demonstration works. (Explaining it to kids)
In our activity the ping pong balls play the role of electrons, the cardboard box plays the role of a metallic surface, and the sand-filled ornaments play the role of photons (or light).
Metalic surfaces have electrons hanging around them bound to the metal. However, for a certain amount of energy they can be hit off. When the electrons are released from the metallic surface they leave behind “holes” (places where electrons ought to be but aren’t). The ejected electrons also create a current, since moving charge is the definition of a current.
In the photoelectric effect, and in this demonstration, energy from incident photons is what kicks these electrons out of their holes. As kids bop the electron ping pong balls some photons will hit the electrons through the holes and create a current.
Other photons (or sand filled ornaments) will not be able to do this. That is because they aren’t heavy enough. The heavier the ornament the more energetic the photon and the more likely it will be able to have enough energy to hit the electron through the hole. This phenomenon is called the threshold frequency!
I hope you enjoyed this fun hands-on method to teach the photoelectric effect to younger students!